fft() on a 2D matrix is the same as
result = zeros(size(YourMatrix));
for column = 1 : size(YourMatrix,2)
result(:,column) = fft(YourMatrix(:,column));
end
That is, it just does a column-by-column fft.
fft2() on a 2D matrix is the same as
fft( fft(YourMatrix).' ).'
That is, it does an fft by columns, transposes that so the rows become columns, fft on those columns, and transpose back
